1. Field of the Invention
The invention relates to safety components for vehicles.
2. Description of the Related Art
The front tracks of motor vehicles are often fitted with a safety device intended to come into play in the event of impact, made up of two assemblies of longitudinal parts placed on each side between the front of the vehicle and the chassis or cradle thereof. At the front, these two assemblies are interconnected by a cross-member referred to as the connecting bar. The connecting bar is itself connected, via two crash cushions, to means for protecting pedestrians, known as pedestrian crossbars or bumpers, located right at the front. The crash cushions are sometimes integrated in the pedestrian crossbar. An assembly of this kind is intended to meet precise specifications as to behaviour in the event of impact.
A longitudinal assembly of this kind most frequently includes the following elements:                a tube having modifications selected so as to comply with the specification for impact at low, moderate and high speed,        an end part, known as the “front plate”, placed at the end of the tube, at the front of the vehicle; this front plate is generally perpendicular to the axis of the tube, or else inclined by a few dozen degrees thereto. It is provided with means enabling other elements to be attached to the front of the vehicle such as the crash cushion, or pedestrian crossbar, for example        opposite it, a second end part located at the rear part of the “tube”. This has the function of positioning, during impact, the component that bears against the chassis or front cradle of the vehicle        and optionally other components.        
The terminology used to designate these components is not totally fixed and there are numerous terms such as “extension”, “extender”, “side member” or “add-on”.
Originally, the term “extension” referred to the tube itself and tube extensions are described in particular in French Patent Applications FR 2 855 805 or FR 2 887 211 of this Applicant. Nowadays, the extension tends to mean the whole assembly and the tube itself is referred to as the “side member”. The word “extender” also tends to mean the assembly as a whole. Similarly, the term “add-on” also tends to mean the assembly as a whole.
In the present application, the word “extension” refers to the whole assembly.
Currently, the elements of the extension are generally steel parts welded together. They may also be made of aluminium.
Crash scenarios are described in the specifications of motor manufacturers. The essential point is the behaviour of the vehicle in a high speed crash; however, it is also important that, in low speed impacts, numerous components including the extension remain substantially undeformed, so that repairs can be carried out simply by replacing the parts that are intended to deform, such as the bumpers. This is what is known as “repairable” impact.
Moreover, in the different scenarios, it is common for the forces absorbed by the components not to be exerted along the axis of the extension. In such cases, the forces exerted on the extension may break down into an axial stress and a torque. This complicates the role of the extension, which is to absorb all or some of the energy generated by the impact.
The components proposed in French Patent Applications FR 2 855 805 or FR 2 887 211 make it possible to respond satisfactorily to different cases of frontal impact, whether they are low speed crashes (or so-called “pedestrian” impacts or “repairable” impacts) or high speed crashes.
The Applicant has set out to provide improvements to the solutions currently in use, notably in the light of different complementary constraints the importance of which has been recognised more recently, and which will be discussed further on.